David T Howe, Rober Gornall, Diana Wellesley, Tracy Boyle, John Barber
Howe D T, Gornall R, Wellesley D, Boyle T, Barber J.
Six year survey of screening for Down's syndrome by maternal age and mid-trimester ultrasound scans
BMJ 2000; 320 :606
doi:10.1136/bmj.320.7235.606